Roadway



J. D. DRURY Aug 13, 1940.

ROADWAY Filed NOV. 28, 1938 i H mw m W@ m mm A @v Patented Aug. 13, 1940UNITED STATES PATENT OFFICE 4 Claims.

This invention relates to roadways.

More particularly it relates to foundations for pavements of roads andother outdoor areas, and to processes for making such foundations.

The invention provides at relatively low cost an improved artificialfoundation or sub-base, which, being laid on a natural foundation ofduly sub-graded ground suitable for a road, and carrying any suitablesuperstructure courses of base, and bedding, binder, or other courses,and Wearing `face surface, should have ability to withstand all ordinarydisturbing influences which may assail the road from any direction-suchas stresses from traffic, weather or Water from above, moisturepenetrating from sides or below, and effects of freezing and thawing.

The importance has long been recognized that the foundation should bepermanent in form and in strength. But in many instances each of suchconstructions has been found imperm-anent, and has soon becomeunsatisfactorily unstable.

The present invention solves the problems of stability and permlanenceby providing a stout waterproof septum completely enveloping andsurrounding the artificial foundation. The term foundation, ashereinafter used, refers to an artificial course under the pavement,unless the context indicates otherwise. This septum comprises acombination having a flexible stout woven fabric impregnated with andencased in a viscid or strongly coherent waterproof substance, and it islaid all around the foundation,- bottom, sides and ton-so as to sealwithin the septum all of that body of earth or other road material whichcomprises the foundation, Waterproofness is thus combined with tensilestrength of enclosure. The fabric holds: the waterproof adheringsubstance in a continuous sheet, flexible but unbroken by bends orstresses. The strength is sufficient in all directions to resistwhatever divisive movement may tend to occur in the granular materialwhich it encloses, While it can flexibly permit sufficient movement forits becoming solidly packed against courses below or above, 'without abreakage of the fabric, and therefore without a breakage of thecontinuity of the thick water seal which the fabric carries. The wholeconstitutes an enduring barrier to all passing of moisture to or from.the compacted material comprised in the foundation.

Illustratively the material for a septum may be a woven strong cloth ofjute impregnated with asphalt and coated on both sides with asphalt.However, other fibrous material might be used, as cotton; and otherwater-repelling sealing material, as resin or rubber. The septum is tobe built into an envelope around the artificial part of the roadfoundation. This may be done by first, laying strips of it, in mutuallylapping formation, on the sub-grade surface of the natural foundation,after that has been suitably prepared and compacted. These strips may belaid with edge portions out-reaching beyond the sides of the excavation,and there turned up. Then, after l the foundation has been installed,the remaining edge parts of the turned-up edge portions are to be turnedback over the top of the foundae tion; and other strips are to be laidonthe top and lapped so that the whole of the top is thus covered.Whatever more, if any, of base is del sired for the pavement, and thecourses for bedding or binding the wearing surface material, and thepavement, are to be built above the foundation thus enveloped andsealed.

Illustratively, the combination of fabric and sealing materialconstituting the septum may have a thickness less than an eighth of aninch. The material of the foundation, surrounded by this strong septum,may often be that ordinary earth of the region, or of the former road,which has been excavated for making the sub-grade.

The sealing material, being material which is not penetrated by water orby air, and being preferably viscid, at least at the timfe when it isapplied, envelops the vegetable fibres of the fabric and permanentlyprotects those fibres from den teriorating effects of water and oxygen,and from organisms living in air or water or in the earth. Preferablythe septum is made of materials which retain flexibility at thetemperatures. which are to be experienced. After it is installed, theconsiderable native tensile strength of the woven or other fabric isenhanced byr the pressing weight of roadmaterial above, and Weight ofpassing traic. The resulting compression of the fabric increases theinternal frictional resistance of threads to slipping over each other,such as must occur before there can be a strain and a breakage. Anytendency of road material With-- in the foundation to slip sidewiseunder displacing pressure from above is resisted, first by the roadmaterial itself, which has inherent frictional resistance toside-slip,-indicated by the angle of repose of its granular element,-andsecond, that granular friction becomes greater under Weight imposed uponit, since the body of slippable material in the foundation is confinedlaterally. Resistance to movemlent is enhanced by the tightcircumscribing effect of the stout fabric, and the fact that trafficweights are applied as forces which tend to flatten the iigure andtherefore to tighten the septum which circumscribes the contents. Inconsequence of this frictional inhibition of internal movement of theencased granular particles, the stress actually experienced by thefabric is greatly diminished from that imposed by traffic at the wearingsurface of the road, and is brought well within the withstanding abilityof the fabric.

The function of the septum, in preventing the entrance of moisture tothe granular material of the foundation, cooperates to maintain theabove-mentioned frictional resistance of that material, for suchresistance is greatest when such material is dry. The describedstructural formation helps dissipate and reduce every ordinary stresswhich might ultimately become imposed on the fabric as a tensilebreaking stress of the textile material. And the textile material bothresists whatever stress ultimately reaches the septum and holds thesealing substance intact.

Assuming the work to be executed well, the strength and shape of fabricwill be permanent; the exclusion of moisture will be permanent; and theroad as a whole will be satisfactory, subject only to effects of traiiicexperience on the wearing surface and the courses above the foundation.

For disclosing the principle, specifications are given below for a roadembodying the invention; but it will be understood that the details thusgiven are illustrative rather than definitive or limiting.

It is intended that the patent shall cover, by suitable expression inthe appended claims, whatever features of patentable novelty exist inthe invention disclosed.

In the drawing:

Figure l is a transverse section through a roadway embodying theinvention, with part broken out so as to make room for showing bothedges of the finished road.

Figure 2 is a fragment of septum, enlarged, in section; and

Figure 3 is a transverse section of an edge portion of the road inprocess of construction.

For illustration, a location having been selected at which the road willhave adequate natural foundation support at bottom and sides, theartiiicial part of the foundation to be built for the new road willcomprise a mass of earth, stone or other body material lll and a septuml2, composite of fabric and sealing material, which rests on thecompacted earth or other firm support I4 which constitutes the naturalfoundation. The said mass is engaged at its sides and top by more of thesame septum I2, so that the mass is enveloped and sealed. Above thesealed envelope is a course of broken stone, coarse or fine, or whateverelse is provided, herein called the base I6, to underlie a wearing topsurface I8, if such a surface course of different construction is alsopresent. An inch or so of gravel, pre-mixed with stone and asphalt, 29,may lie between this base i6 and the sealed foundation I0.

The materials, arrangement and dimensions of these various parts aresubject to engineering judgment of the designer.

While it is expected that for most roads a base course will rest on thefoundation, which will be the sealed element, there may be other roadconstruction employing the invention by building the surface coursedirectly upon the sealed element, or otherwise arranging the elementswhilegetting the benefits of the sealing septum herein described.

The septum may be prepared by thoroughly saturating a strong fabric,preferably jute or cotton closely woven, with hot asphalt cement, thesaturated fabric being rolled or compressed in order to assure thethorough entering of the asphalt into the fabric, between the threads,and the sealing of the mesh openings. Then the fabric while Wet from thesaturation should receive a film of hot asphalt not less than 1,(,4 ofan inch thick on each side of the fabric, over the entire area of thefabric, temperature of the asphalt cement during the saturation and thefilm application being maintained in the range 20D-225 F., making aseptum which when in place will have a thickness of the order of 335 ofan inch.

The septum is represented in Figure 2, where a is the textile fabric andb is the continuous body of waterproof adhesive plastic material,covering both surfaces and reaching in between threads and betweenfibres.

The septum having been prepared in strips which for convenience ofhandling are preferably not more than 120 inches wide, 50 to 100 yardsin length, a strip of the septum is to be laid along the bottom of theexcavation, extending out sidewise and upward over the slope ol' theshoulder suiiiciently to permit the ultimate folding back of this edgeportion of the septum, over the tcp of the foundation to a substantialwidth, for which 18 inches is suggested as being sufficient, althoughmuch less would serve.

The next strip of septum is then placed on the sub-grade, lapping a fewinches, for example, four inches, over the first strip and firmlycemented thereto with hot asphalt cement. This procedure is to continueacross the roadbed until the bottom of the excavation has been coveredand both sides have extensions sufficient for the folding back of theseptum later, over the foundation, to the desired extent. Wooden moldforms, 22, may be set along the edges of the excavation as indicated inFigure 3 to shape the edges of the filling which is to constitute theroad; the edge part of the septum strip l2 being bent up to line themold, for vertical or other desired edge surface.

The material which is to constitute the foundation lll is then to beplaced on the septum in the excavated area, shaped, brought to thespecified grade, and thoroughly compacted. If earth or other granularmaterial is employed for this the strength of the resulting foundationwill be greater if it has low content of moisture when sealed, which maybe attained or assured, if necessary, by heating it in open air justbefore puting it into the foundation. The edge portions of the septumwhich have been left extending over the side molds on both edges of theroad are then to be folded back over the top of the foundation; and theseptum is to be laid on that top in mutually overlapping strips, as atthe bottom. Such base course and other courses as may be predeterminedare then to be constructed above the upper septum. This can beconstructed directly upon the septum, or, if it is to be of brokenstone, an inch or so of earth or other cushioning material may bepreferably first be laid on the septum. The ends of the project are tobe sealed by enveloping the end of the foundation within the septum,like the sides.

A successful construction of fabric for the septum is found in a plainweave of cotton or jute, the yarns being single and Without sizingapplied to any part of the fabric. Such a fabric vcontaining 180 ends in12 inches and 144 picks in 12 inches may have an A. S. T. M. breakingstrength averaging -100 pounds in the warp and like strength in filling.The asphalt used may be of the rapid curing type customary for sheetasphalt in pavements according to standard specication known as RC 3.Specifications of both may be varied.

Jute or cotton is suggested for the fabric be-4 cause these are bases towhich asphalt cement vwill adhere, and which have strength to retain theasphalt in place as a water barrier regardless of the nature of thesoil, and will provide a strong and flexible septum which will be ableto withstand the stresses occasioned by differential movements, and byimpact of trafic. The ultimate requirement is that the septum bewaterproof, tough and durable, having a breaking strength greater thanis ordinarily to be imposed horizontally upon it by any stresses in thehigher courses of the road, or by any stresses arising between theartificial foundation and the soil below which constitutes the naturalfoundation. It will be observed that if the latter is stable, the septumresting on it becomes adhesively and frictionally secured both to it andthe articial foundation which the septum envelope, and is itself subjectordinarily only to compressive stresses. Stresses emanating from anyparticular point of heavy pressure on the surface of the road becomeconsiderably spread and distributed, and so are minimized in intensity,before they reach the septum; and such stresses are resisted byneighboring portions of the foundation and septum as well as by thoseportions which are more directly underneath the point whence the stressemanates. This secure strength never becomes reduced by the entry ofwater into the foundation by capillary attraction from below, or byinfiltration from above or beside, even under extremes of climatic ortemperature conditions. The applying of pressure at any point on thesurface of the top course of the septum tends to deform the containedmass into a thinner rectangle, whose perimeter would be greater, sothat, theoretically, if any movement within the septum were to occur,tension would thereby be generated in the septumy to resist suchmovement, and the mass automatically increases its friction to arrestsuch a movement. Therefore it is not necessary to use expensive crackedstone or gravel for the foundation, but the same soil which has beenexcavated from the pre-existing road can be used to constitute thefoundation because, when so located, the septum will keep it free fromwater and will contribute to its stabilization.

Asphalt has been mentioned for the waterproof seal as it has the neededqualities, is of low cost, and is a familiar and abundant road material;but rubber and resins each may be used, being taken in suitableconsistency for penetration, adhesiveness, and ultimate waterproofness,and so may any other materials having the requisite described qualities.

In either case, and in either process of construction above indicated, awatertight bond is eiected between the sealed course, and the subgradeor course, if any, below it, and between the sealed course and thematerial placed upon it.

The excluding of water from the sealed artificial foundation makes lessdangerous the presence of water in the natural foundation under it;therefore some sub-drainage heretofore necessary in preparing thesub-grave can be omitted.

The invention thus makes savings in cost, over practices hithertoprevalent, in that its requirements are less both in excavation, indrainage, inexpense of foundation material, in base course material, andin maintenance costs. v

The embodiment of the invention herein illus tratively presented may beconsidered as having the septum in four sections, two of which are theunder and upper. courses of septum and two of which are those whichstand upright at the sides of the road, the best form of the inventionbeing that in which the entire artificial foundation is surrounded andsealed against moisture passing in or out. The side sections, those atthe edges of the road, are not necessarily so perfectly upright as arerepresented in the drawing. In some cases, if the terrain is reasonablydry, and especially if the side edges of the foundation are otherwiseprotected against the entrance of moisture, these upright sections maybe omitted, and a measure of envelopment, probably suiicient for themiddle part of the road, will be had from the overlying and underlyinghorizontal septum layers.

The invention has been illustratively described as it may be applied inroadway construction, this being the field in which its use wouldprobably be most extensive; ybut it will be understood that it can alsobe used with advantage for pavements of other areas, as driveways, yardsand courts, including tennis courts, public squares, and all p-lacesexposed to Weather and to infiltration of water from beside or below;also for revetments on river banks, banks at road cuts and other banksexposed to wash by water; and also in connection with foundations forbuildings where packed granular material is used,

I claim as my invention:

1. In a pavement structure having a plurality of superimposed courses ofroad making material, that improvement in which an under one of saidcourses is a conned body of loose earthy or the like road material withconstant content of moisture; there being a permanent, conning septum,sealed completely around that said body and its moisture; said septumcomprising a flexible sheet, having a continuous body of material whichis inert to the chemical properties and biological content of ordinaryearth and is impervious to moisture, and said sheet having toughness andtensile strength oi an order suitable for flexibly withstanding thedeformation stresses to which the said course is normally subject fromimposed weights and tran-lc and from movements of subadjacent earth,whereby the septum is of permanent nature and maintains constant themoisture f content of the surrounded earthy material.

2. In a pavement structure, an improvement as in claim 1 in which theseptum is a woven strong fabric combined with a plastic substance of anature impervious to moisture and to microorganisms, spread over bothsides of the woven fabric, adhering thereto and coalesced thereon.

3. In a pavement construction, a combination as in claim 1, in which theseptum is a composite sheet comprising a strongly cohering woven fabricsheet and a coating of viscid waterproof material adhering thereto.

4. In a pavement construction, a combination as in lclaim l, in whichthe septum is a composite sheet comprising a. woven fabric and asphaltadhering thereto; the fabric sheet being both impregnated with asphaltand coated on both sides with asphalt,

JOHN D. DRURY.

